Between November 1939 and July 1943, the U-boat conducted 14 combat patrols, sinking 21 merchant ships for a total of 117,036 gross register tons (GRT), damaging one ship of 10,350 GRT and another of 9,131 GRT - enough for it to be declared a total loss.

U-43 was sunk on 30 July 1943 southwest of the Azores by a torpedo dropped by a United States Navy aircraft; all 55 hands were lost.[5]

Like all Type IXA submarines, U-43 had two MAN M 9 V 40/46 supercharged 9-cylinder diesel engines that put out 4,400 hp (3,281 kW) as well as two SSW 2 GU 345/34 double-acting electric motors that produced 1,000 hp (746 kW) and allowed her to travel at up to 18.2 knots (33.7 km/h; 20.9 mph) while surfaced and 7.7 knots (14.3 km/h; 8.9 mph) submerged. She had a range of 10,500 nmi (19,400 km; 12,100 mi) at 10 knots (19 km/h; 12 mph) while on the surface and 65–78 nautical miles (120–144 km; 75–90 mi) at 4 knots (7.4 km/h; 4.6 mph) while submerged. U-43 had six torpedo tubes, (four in the bow, two in the stern). She also carried a total of twenty-two 53.3 cm (21 in) torpedoes and had a 10.5 cm (4.1 in) SK L/45 deck gun and 180 rounds. She was equipped with one 3.7 cm (1.5 in) and one 2 cm (0.79 in) anti-aircraft gun. U-43 had a crew of 55 men; however, she could hold up to 56 crew members at any given time. After being commissioned and deployed, U-43 was stationed in the German port city of Wilhelmshaven.[3]

Commissioned into the 6th U-boat Flotilla, based at Kiel,[1]U-43 left for her first combat patrol of the war on 6 November 1939, sailing around the British Isles and into the Atlantic.[6] There, on 16 November, she attacked the 4,915 ton British merchant ship Arlington Court, a straggler from Convoy SL-7A, en route from Rosario, Argentina to Hull with a cargo of 7,340 tons of maize. The ship was hit by a single torpedo 320 nautical miles (590 km; 370 mi) west-south-west of Start Point in Devon. The crew abandoned ship, the U-boat fired another torpedo, which sank the ship within 30 minutes. Seven of the crew were lost, the survivors were picked up by Dutch and Norwegian freighters.[7] After the attack, U-43 was hunted by convoy escorts for 20 hours, sustaining some damage from depth charges.[1]

Continuing with her patrol, U-43 attacked Convoy 14-BS in the Bay of Biscay, and sank the 4,374 ton French merchant ship Arijon on 22 November.[8] Convoy escorts counter-attacked with 23 depth charges, but U-43 escaped without damage.[1]

Late on 25 November 1939, about 120 nautical miles (220 km; 140 mi) west-north-west of Cape Finisterre (northwest Spain), U-43 attacked the unescorted 2,483 ton British collierUskmouth. Both G7a torpedoes malfunctioned (a common problem in the early years of the war), so the U-boat opened fire with her deck gun. After a while she fired another torpedo, but missed, so recommenced shelling. After firing 149 rounds, U-43 left the ship on fire and slowly sinking. Two crewmen were killed, while 23 survivors were picked up by an Italian merchant ship.[9]

On the morning of 8 December U-43 was attacked by an unidentified aircraft and severely damaged.[1] She returned to Wilhelmshaven six days later, on the 14th.[4]

After the 6th U-boat Flotilla was disbanded in December 1939, U-43 was assigned to the 2nd U-boat Flotilla based in Wilhelmshaven. U-43 departed from there on 13 March 1940 and sailed along the coast of Norway, north of Scotland, and into the waters west of Ireland, but had no success.[10] The First Watch Officer (second-in-command of the U-boat) Oberleutnant zur See Hans-Wilhelm Behrens fell overboard and was lost on 31 March.[1]U-43 returned to Wilhelmshaven, after 25 days at sea, on 6 April.[4]

U-43 '​s third voyage began on 12 April 1940. She patrolled the North Sea and along the Norwegian coast, supporting the invasion of that country.[11] On 22 April she was bombed by two British Hudson aircraft and suffered slight damage.[1] She returned to Wilhelmshaven the next day.[4]

U-43 sailed from Wilhelmshaven on 13 May 1940 and out into the Atlantic.[12] Her first attack took place on 28 May, south-west of Land's End, when she fired a torpedo at the British merchant ship Alca. She missed, and then opened fire with her deck gun. The armed ship returned fire, but neither vessel made any hits; the U-boat broke off the attack.[1]

U-43 finally found success on 21 June when she attacked Convoy 65-X south-west of Figueira da Foz, Portugal, hitting the 8,627 ton British tankerYarraville with a single torpedo. The ship caught fire and sank. Five crew members were killed, the 45 survivors were picked up by a French trawler.[13]

Late on 30 June U-43 hit the 13,376 ton British merchant ship SS Avelona Star with a single torpedo 220 nautical miles (410 km; 250 mi) northwest of Cape Finisterre. The ship, part of Convoy SL-36, was en route from Buenos Aires to London with a cargo of 5,630 tons of frozen meat and 1,000 tons of oranges. The crew abandoned the ship, which foundered the next day. One crewman was killed in the attack, the 84 survivors were picked up by the British merchant ship Beignon, which was subsequently torpedoed and sunk by U-30 on 1 July. Three survivors from Avelona Star were killed.[14]

On the evening of 9 July U-43 sank the unescorted 3,944 ton British merchant ship Aylesbury about 200 nautical miles (370 km; 230 mi) southeast of Ireland. Hit by two torpedoes, the ship sank in 15 minutes. All 35 crew survived.[15]

U-43 '​s fourth and final success on her fourth patrol took place on the morning of 17 July when she sank the 3,509-ton British merchant ship Fellside, a straggler from convoy OA-184, about 135 nautical miles (250 km; 155 mi) north-west of Bloody Foreland (Cnoc Fola), Donegal. The U-boat's first torpedo passed under the vessel, but the second struck the ship and caused her to sink within five minutes. Twelve of the crew were killed, 21 survivors were rescued.[16]U-43 arrived back at Wilhelmshaven on 22 July after 71 days at sea.[4]

U-43 sailed from Wilhelmshaven on 9 September 1940, stopping at Bergen, Norway for three days before sailing on the 15th for another Atlantic patrol.[17] She sank only one ship, the 5,802 ton British merchantman Sulairia, separated from Convoy OB-217, on 25 September. The U-boat hit the ship with a single torpedo causing her to sink 356 nautical miles (659 km; 410 mi) west of Achill Head, County Mayo.[18] One man was lost, the remaining 56 crewmen were picked up by HMCS Ottawa.[19]

Under her new captain, U-43 left Lorient on 10 November 1940 and returned to the waters west of Ireland, where she sank three more merchant ships and damaged a fourth.[23]

On the morning of 2 December she attacked Convoy OB-251 west-south-west of Rockall and sank two ships. Her first victim was the 7,113 ton British merchant ship Pacific President, which was hit by two torpedoes and quickly sank with the loss of her crew of 50 men.[24] Forty-five minutes later U-43 hit the 12,247 ton British oil tankerVictor Ross with two torpedoes. A third torpedo was fired five minutes later, but missed, the U-boat evaded a ramming attempt by crash-diving shortly afterwards. However, she persisted and hit the ship with a fourth torpedo 20 minutes later, sinking her. There were no survivors from her 44 crew.[25]

In the evening of 6 December, U-43 spotted a ship and pursued her for three and a half hours before firing a single torpedo, which missed. The U-boat fired another torpedo 20 minutes later, hitting the unknown ship and sinking her in 63 seconds. The vessel is believed to be the 1,902 ton Norwegian merchant ship Skrim, which had lost contact with Convoy OB-252 two days before in heavy weather and was never seen again.[26]

Finally, on 13 December, U-43 fired two torpedoes at the unescorted 10,350 ton British merchant ship Orari about 450 nautical miles (830 km; 520 mi) southwest of Ireland. One torpedo hit the ship in the stern. However, U-43 had no torpedoes left, and the sea was too rough for her to use her deck gun. The crew of the ship managed to plug the hole with tarpaulins, and the ship made it under her own power to the Clyde.[27]

U-43 returned to Lorient on 17 December 1940 after a patrol of 38 days.[4] On 4 February 1941, while at Lorient docks, U-43 was sunk after a valve was accidentally left open, putting the U-boat out of action for the next three months.[1]

After this enforced absence U-43 began her next patrol on 11 May 1941, still under the command of Wolfgang Lüth, who had been promoted to Kapitänleutnant on 1 January.[28] Once again she sailed out into the mid-Atlantic, where she sank three ships.[29]

Early on the morning of 15 May U-43 opened fire with her deck gun and anti-aircraft guns on the 488 ton French three-masted sailing ship Notre Dame du Châtelet, en route from St. Malo to the Grand Banks of Newfoundland to fish. After being hit by 45 shells the ship sank. Lüth suspected that the vessel was reporting the positions of U-boats to Allied forces, while the 10 survivors thought they had been attacked by a British submarine. They, from her crew of 38, abandoned ship in two lifeboats. Two were picked up by the Italian submarine Otaria on 23 May.[30]

On the evening of 6 June U-43 put two torpedoes into the 4,802 ton Dutch merchant ship Yselhaven about 600 nautical miles (1,100 km; 690 mi) east of Newfoundland. The ship, separated from Convoy OB-328, sank within two minutes. Only 10 of her crew of 34 survived to be rescued by the Finnish merchantman Hammarland on 15 June.[31]

In the early hours of 17 June, U-43 torpedoed and sank the 2,727 ton British merchant ship Cathrine, part of Convoy SL-76, which was loaded with 3,700 tons of manganese ore, about 250 nautical miles (460 km; 290 mi) south-west of Cape Clear (southern Ireland). Only three men survived from her crew of 27; they spent 33 days in a lifeboat before being found by a British trawler.[32]

U-43 '​s next patrol, beginning on 2 August 1941, took her back out into the mid-Atlantic for 53 days, but she had no success before returning to Lorient on 23 September.[33]

U-43 went to sea again on 10 November 1941, this time she was more successful, sinking three ships near the Azores.[34]

Early on the morning of 29 November, U-43 fired two torpedoes at the 5,569 ton British merchant ship Thornliebank, part of Convoy OS-12, and loaded with general cargo and munitions, about 240 nautical miles (440 km; 280 mi) north-north-west of the Azores. Both torpedoes struck the ship, which exploded violently. There were no survivors from the crew of 75 men. Despite being about 1,200 metres (0.75 mi) distant, debris from the explosion struck the surfaced U-boat, slightly injuring a crewman; the next day an unfuzed 10 cm (3.9 in) shell was found lodged in the conning tower.[35]

On the evening of 30 November, the 4,868-ton British merchant ship Ashby, a straggler from Convoy OS-12, was hit by one of two torpedoes fired by U-43, 170 nautical miles (310 km; 200 mi) south-south-east of Flores in the Azores. The ship sank within four minutes with the loss of 17 of her crew of 50. The survivors were picked up by the Portuguese destroyer Lima.[36] After the attack the U-boat was depth charged for several hours by convoy escorts, but managed to escape unharmed.[1]

At about 17:00 on 1 December 1941, U-43 and U-575 spotted the 7,542 ton unescorted and unarmed tanker Astral. Both U-boats gave chase, but after four hours U-575, commanded by KapitänleutnantGünther Heydemann, observed the large American flag painted on her side and abandoned the pursuit. U-43 continued to follow the neutral ship, firing a torpedo at her around midnight, which missed. The ship immediately began to sail a zigzag evasive course at full speed, but the U-boat had no problem following her in the light of the full moon. The next morning U-43 hit the Astral with two torpedoes. The ship, loaded with 78,200 barrels (12,430 m3) of gasoline and kerosene, exploded and sank within minutes. There were no survivors from her crew of 37. The Astral was the third of four American merchant ships sunk by U-boats prior to America's entry into the war.[37]

Lüth's last patrol with the boat began on 30 December 1941, when U-43 sailed from Lorient into the mid-Atlantic, where she sank three more ships.[38] The first was the 5,246 ton Swedish cargo ship Yngaren, straggling from convoy HX-168 due to bad weather, about 600 nautical miles (1,100 km; 690 mi) west of Ireland. On the morning of 12 January 1942 the ship was hit by two torpedoes and sank within a minute. Six British passengers and 32 crewmen were lost, the only two survivors were spotted on a raft on 10 February by a British patrol aircraft, which directed a fishing trawler to their position the next day.[39]

Early in the morning of 14 January, U-43 attacked Convoy ON-55 south of Iceland and sank the 6,641 ton British merchant ship Empire Surf. Only six of the crew of 53 survived to be picked up by HMS Alisma.[40] About two hours later U-43 attacked the convoy again and sank the 5,707 ton Panama-registered American merchant ship Chepo. There were 21 survivors from her 38 crew.[41]

The U-boat then sailed to Kiel, arriving on 22 January. Command of the U-boat passed to her 1.WO, Oberleutnant zur See Hans-Joachim Schwantke, as Lüth left to commission U-181.

U-43 '​s first patrol under her new commander began on 4 July 1942, as she sailed from Kiel via the 'gap' between Iceland and the Faroe Islands into the mid-Atlantic. However, she achieved no success, and arrived back at Lorient on 15 August after 43 days at sea.[42]

On the morning of 18 November, U-43 fired four torpedoes at Convoy SC-109 and hit the 9,131 ton American tanker Brilliant, loaded with 90,704 barrels (14,420.8 m3) of fuel oil. A 40-foot (12 m) diameter hole was made in her side, and the cargo caught fire. While some of the crew abandoned ship, those remaining aboard managed to put the fires out; making only three knots, the ship limped the 300 nautical miles (560 km; 350 mi) to Bonavista Bay, Newfoundland, arriving on 24 November. Brilliant eventually left Newfoundland on 18 January 1943 under tow, but after two days the ship broke in half. The fore section sank immediately, while the aft section drifted for some days before it was found and the 44 crew rescued. The aft section was taken in tow, but sank the next day.[44]U-43 arrived back at Lorient on 9 December after a patrol of 78 days.[4]

U-43 '​s first patrol of 1943 began on 9 January, patrolling the waters between the Azores and the West African coast.[45] On 3 March she spotted a vessel, identified it as a British Blue Star Line merchant ship, and hit it with three torpedoes, it sank it within two minutes. Only later did U-43 learn that it was the 5,154 ton German blockade runner Doggerbank, formerly the British Speybank that had been captured by the auxiliary cruiserAtlantis in January 1941. The ship was carrying 7,000 tons of rubber, fats, fish oil, and other raw materials from Yokohama to France; she was several days ahead of her scheduled arrival date.[46]

U-43 '​s final patrol began when she sailed from Lorient on 13 July 1943 and headed southwest into the Atlantic.[4] On the evening of 19 July, in company with U-403 in the Bay of Biscay, the two U-boats were attacked by a British Liberator Mk.V bomber of No. 86 Squadron RAF. U-403 crash-dived immediately, covered by the AA fire of U-43, which then dived. The Liberator was slightly damaged and a crewman wounded, but dropped two homing torpedoes. Neither U-boat was damaged and both escaped.[1]

During her service in the Kriegsmarine, U-43 sank 21 merchant ships for a total of 117,036 GRT, damaged one vessel of 10,350 GRT, and another of 9,131 GRT - enough for it to be declared a total loss.[48]